Biogas slurry advanced treatment and biogas purification combined method and system

Abstract

The invention discloses a biogas slurry advanced treatment and biogas purification combined method and system, and belongs to the technical field of environmental engineering wastewater treatment.The biogas slurry is pumped into a mixing pool, ferroferric oxide and a ferrite solution are added, the mixture flows into an oxidation pool, after an oxidizing agent is added, the mixture flows into a nucleation pool, alkaline calcium is added, and magnetic calcium-iron layered double hydroxide nucleation occurs; the biogas slurry enters an aging tank to complete crystallization and solidify phosphorus, iron and calcium in the biogas slurry, meanwhile, carbon dioxide removal biogas is introduced to blow off ammonia and absorb sulfur, ammonia is recycled by an ammonia absorption tower, and purified biogas is obtained. Alkaline biogas slurry containing the magnetic composite material is pumped into a magnetic sedimentation tank from an aging tank and settled under the action of a magnetic field, supernate flows into an alkaline water tank to absorb carbon dioxide in the biogas to generate calcium carbonate, and the biogas slurry is pumped into the sedimentation tank for calcium carbonate sedimentation. According to the method, the biogas slurry can be deeply treated, the biogas can be purified, no sludge is generated, and the magnetic calcium-iron layered double-metal hydroxide nanocomposite, calcium carbonate and ammonia fertilizer can be produced.

Description

Technical Field

[0001] The invention belongs to the technical field of environmental engineering wastewater treatment and renewable energy, and relates to a biogas purification method and system for biogas slurry deep treatment. Background Art

[0002] Biogas fermentation technology is an effective means of treating organic waste and high-concentration organic wastewater. It can not only degrade organic pollutants, but also produce renewable energy - biogas, and has multiple greenhouse gas emission reduction effects. The biogas slurry produced by biogas fermentation is rich in organic compounds and nutrients such as nitrogen and phosphorus. Since most biogas projects lack sufficient land to absorb biogas slurry, biogas slurry needs to be treated to meet standards (deep treatment). In recent years, advanced oxidation technologies (such as Fenton and persulfate advanced oxidation technologies) can oxidize organic matter into carbon dioxide, water, inorganic salts, etc., with good treatment effects and short time, and are highly efficient for deep treatment of biogas slurry with poor biodegradability. Ferrous ions have the advantages of high activity, easy availability, and low price, and are one of the most commonly used catalysts in advanced oxidation technologies. However, advanced oxidation based on ferrous ions requires strong acidic conditions (pH=3~4), so that the wastewater needs to be adjusted to the required pH (6~9) with alkali before discharge; in addition, a large amount of iron sludge will be produced during the reaction, which poses a potential risk of environmental pollution and has high post-treatment costs. If it is disposed of as waste, it will cause a waste of iron resources.

[0003] On the other hand, advanced oxidation has limited ability to remove inorganic pollutants (such as ammonia nitrogen and inorganic phosphorus) in biogas slurry. Ammonia recovery technology in biogas slurry has opened up new ways for the removal and utilization of ammonia nitrogen in biogas slurry. The most commonly used ammonia recovery process is ammonia stripping-acid absorption. Generally, gases (air, water vapor, exhaust gas, etc.) are passed into the biogas slurry, and the ammonia nitrogen in the biogas slurry is converted into gaseous NH3. Then, the volatile ammonia is selectively absorbed by the absorption liquid. Generally speaking, the biogas slurry needs to be pretreated before stripping, usually with a strong alkali (CaO, Ca(OH)2, NaOH) to alkalize it to a pH value of about 10, or the biogas slurry temperature is increased by heating to promote the volatilization of NH3.

[0004] The main components of biogas produced by biogas projects are methane (60~80%) and carbon dioxide (20~40%). Carbon dioxide has a low calorific value and accounts for a large proportion, which increases the cost of long-distance transportation and is not conducive to the high-value utilization of biogas. Therefore, before using it as urban gas or vehicle gas, biogas needs to be purified. The main methods for biogas purification include pressure swing adsorption, water washing, amine washing, membrane separation, etc. However, the equipment investment for these methods is relatively large. In addition, a small amount of hydrogen sulfide (100~10000 mg / m 3 ) gas is produced, which is toxic and easily causes corrosion to pipelines, instruments, equipment, etc. Therefore, appropriate measures need to be taken to desulfurize the biogas.

[0005] In summary, the existing technologies have the following problems: (1) The amount of sludge produced by iron-catalyzed advanced oxidation treatment of biogas slurry is large and the treatment cost is high; (2) Iron-catalyzed advanced oxidation, which works better under acidic conditions, requires alkali to adjust the pH; (3) Advanced oxidation has poor removal effect on ammonia nitrogen and total phosphorus in biogas slurry; (4) Ammonia stripping of biogas slurry requires alkalization; (5) Acidic gases such as carbon dioxide and hydrogen sulfide need to be removed from biogas for purification. A comprehensive solution is needed to remove COD, ammonia nitrogen, and total phosphorus from biogas slurry and remove carbon dioxide and hydrogen sulfide from biogas, while solving the problems of deep biogas slurry treatment and biogas purification. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a method and system for deep treatment of biogas and combined biogas purification, thereby effectively removing COD, ammonia nitrogen, total phosphorus in biogas and carbon dioxide and hydrogen sulfide in biogas, and can also produce high value-added products such as magnetic calcium-iron layered double hydroxide nanocomposites, calcium carbonate, ammonia fertilizer, etc., to achieve the effects of deep treatment of biogas and purification of biogas without generating sludge.

[0007] The present invention is achieved through the following technical solutions: A biogas purification method for biogas slurry deep treatment, characterized by comprising: S1. Adding ferroferric oxide, ferrous salt solution and oxidant to biogas slurry to generate advanced oxidation reaction, thereby degrading pollutants in biogas slurry, then adding alkaline calcium reagent to perform nucleation reaction of magnetic calcium iron layered double metal hydroxide, then introducing decarbonized biogas to blow off ammonia in biogas slurry, and after sulfur in biogas is absorbed, obtaining decarbonized, desulfurized and ammonia-containing biogas, and performing crystallization reaction of magnetic calcium iron layered double metal hydroxide to solidify inorganic phosphorus, iron and calcium in biogas slurry; S2, mixing the decarbonized, desulfurized, ammonia-containing biogas with the ammonia generated by the nucleation reaction and performing ammonia absorption treatment with an acid solution to obtain decarbonized, desulfurized, and deammonified purified biogas; S3, after the biogas slurry after the crystallization reaction is precipitated, the solid magnetic calcium iron layered double metal hydroxide is separated from the bottom precipitate, the upper calcium-containing alkaline biogas and the original biogas are subjected to carbon dioxide absorption to obtain decarbonized biogas, and the calcium in the calcium-containing alkaline biogas is solidified to obtain purified biogas containing calcium carbonate; S4. Separate the solid calcium carbonate from the bottom sediment in the purified biogas slurry containing calcium carbonate, and obtain the upper layer of biogas slurry with organic pollutants, nitrogen and phosphorus removed, which is discharged / recycled, thereby achieving deep treatment of biogas slurry combined with biogas purification.

[0008] Preferably, the ferroferric oxide is magnetic ferroferric oxide nanoparticles; the ferrous salt is one of ferrous chloride, ferrous nitrate and ferrous sulfate; the oxidant is one of hydrogen peroxide, hypochlorite, persulfate and peracetic acid; The molar concentration of the ferrous salt solution is greater than or equal to 30 mmol / L; the amount of ferroferric oxide added is 0.5-5 g / L; the alkaline calcium reagent is calcium oxide or calcium hydroxide; and the molar ratio of the alkaline calcium reagent to the ferrous salt is 2-4:1.

[0009] Preferably, the time of the advanced oxidation reaction is 10-30 min, the time of the nucleation reaction is 5-20 min, the pH of the nucleation reaction is 10-13, the time of the crystallization reaction is 40-100 min, the time of the biogas slurry precipitation after the crystallization reaction is 10-30 min, and the volume ratio of the decarbonized biogas to the biogas slurry is 200-400:1.

[0010] A biogas purification system for biogas slurry deep treatment, comprising: Biogas tank, mixing tank, oxidation reaction tank, nucleation tank, aging tank, magnetic sedimentation tank, alkaline water tank, decarbonization tower, sedimentation tank, raw biogas storage tank, ammonia absorption tower, acid storage tank and purified biogas storage tank; The biogas slurry pool is connected to a mixing pool, an oxidation reaction pool, a nucleation pool, an aging pool, a magnetic sedimentation pool, an alkaline water pool, a decarbonization tower and a sedimentation pool in sequence; The bottom of the aging tank is connected to the top of the decarbonization tower through a pipeline; the top of the nucleation tank and the aging tank are connected to the bottom of the ammonia absorption tower; the acid storage tank is connected to the ammonia absorption tower; The purified biogas storage tank is connected to the ammonia absorption tower; the raw biogas storage tank is connected to the bottom of the decarbonization tower; The mixing pool is connected to the drug dissolving pool 1 through a pipeline; the oxidation reaction pool is connected to the drug dissolving pool 2 through a pipeline; and the nucleation pool is connected to the drug dissolving pool 3 through a pipeline.

[0011] Preferably, the nucleation pool is a covered and sealed pool, the top of which is provided with a through hole, and is connected to the ammonia absorption tower through an alkali-resistant pipe, and the inner wall of the nucleation pool is made of alkali-resistant material; the aging pool is a covered and sealed pool, the top of which is provided with a through hole, and is connected to the ammonia absorption tower through an alkali-resistant pipe, and the inner wall of the aging pool is made of alkali-resistant material; the alkaline water pool is a covered and sealed pool, and the inner wall of the alkaline water pool is made of alkali-resistant material.

[0012] Preferably, the top pipeline of the decarbonization tower is connected to the decarbonization biogas pipeline of the aging tank and the purified biogas pipeline of the purified biogas storage cabinet, and a check valve is installed between the connection and the decarbonization tower; A gas flow meter 1 is provided on the connecting pipeline between the raw biogas storage tank and the decarbonization tower; A gas flow meter 2 is provided on the connecting pipeline between the purified biogas storage cabinet and the aging tank; The bottom of the magnetic sedimentation tank is connected to a solid-liquid separator 1; the bottom of the sedimentation tank is connected to a solid-liquid separator 2.

[0013] Preferably, a magnetic field is provided at the bottom of the magnetic sedimentation tank.

[0014] Preferably, the decarbonized biogas and the purified biogas are introduced from the bottom of the aging tank, and the internal pipes for introducing the decarbonized biogas and the purified biogas from the bottom of the aging tank are multiple evenly distributed porous pipes.

[0015] Preferably, the raw biogas in the raw biogas storage tank is introduced from the bottom of the decarbonization tower, and the internal pipeline for introducing the raw biogas from the bottom of the decarbonization tower is a plurality of multi-microporous tubes; the empty tower residence time of the raw biogas in the decarbonization tower is 0.5-2 min; the pH value of the solution in the decarbonization tower is maintained at 7-9.

[0016] Preferably, when the decarbonized biogas in the decarbonization tower is insufficient, the decarbonized biogas is distributed from the purified biogas storage cabinet through gas flow meter 2.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention provides a method for deep treatment of biogas combined with biogas purification, which degrades pollutants in biogas by iron-catalyzed advanced oxidation, and then prepares a high-value-added magnetic calcium-iron layered double metal hydroxide composite material by adding cheap alkaline calcium, fully recovers iron resources, avoids the generation of iron mud, and overcomes the problem of large iron mud output in iron-catalyzed advanced oxidation technology. By utilizing the characteristic that biogas becomes alkaline due to the addition of alkaline calcium, alkaline biogas is used to absorb acidic gases in biogas, such as carbon dioxide and hydrogen sulfide, so that the biogas effluent is within the emission standard range. Decarbonized biogas and purified biogas are circulated back to blow off ammonia in alkaline biogas, and the ammonia is recovered. The present invention can not only remove biogas COD, ammonia nitrogen, total phosphorus, and carbon dioxide and hydrogen sulfide in biogas, but also produce high-value-added products such as magnetic calcium-iron layered double metal hydroxide nanocomposites, calcium carbonate, and ammonia fertilizer, while achieving deep treatment of biogas, biogas purification, and no sludge generation.

[0018] Furthermore, when the decarbonized biogas is insufficient, the decarbonized biogas is distributed from the purified biogas storage cabinet through gas flow meter 2, and the purified biogas pipeline distributed from the purified biogas storage cabinet is connected to the decarbonized biogas transportation pipeline, and a check valve is installed on the pipeline between the connection and the top of the decarbonization tower to prevent the distributed purified biogas from entering the decarbonization tower when the amount is large.

[0019] Furthermore, the decarbonized biogas and purified biogas of the present invention are introduced from the bottom of the aging tank. The internal pipes for introducing the decarbonized biogas and purified biogas from the bottom of the aging tank are multiple evenly distributed porous tubes, which can play a role of uniform and slow stirring, which is conducive to the rapid crystallization of magnetic calcium iron layered double metal hydroxides.

[0020] Furthermore, the inner wall of the magnetic sedimentation tank of the present invention needs to use alkali-resistant materials; the inner wall of the alkaline water pool needs to use alkali-resistant materials, and the pool is covered and sealed to prevent the absorption of carbon dioxide in the air. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the connection of facilities and equipment involved in the process flow of the present invention.

[0022] The markings in the figure are: 1. Biogas slurry tank; 2. Mixing tank; 3. Drug dissolving tank 1; 4. Oxidation reaction tank; 5. Drug dissolving tank 2; 6. Nucleation tank; 7. Drug dissolving tank 3; 8. Aging tank; 9. Magnetic sedimentation tank; 10. Solid-liquid separator 1; 11. Alkaline water tank; 12. Decarbonization tower; 13. Sedimentation tank; 14. Solid-liquid separator 2; 15. Original biogas storage tank; 16. Ammonia absorption tower; 17. Acid storage tank; 18. Purified biogas storage tank; 19. Gas flow meter 1; 20. Gas flow meter 2; 21. Check valve. DETAILED DESCRIPTION

[0023] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.

[0024] A method and system for deep treatment of biogas combined with biogas purification, wherein biogas is pumped from a biogas pool into a mixing pool, magnetic ferroferric oxide nanoparticles and a ferrous salt solution are added thereto, the mixture is evenly mixed, and then the biogas flows into an oxidation reaction pool, an oxidant is added thereto, an advanced oxidation reaction occurs, and pollutants in the biogas are degraded and removed; the biogas from which most pollutants have been removed flows into a nucleation pool, alkaline calcium is added thereto, magnetic calcium-iron layered double metal hydroxides are nucleated, and then the biogas flows into an aging pool, further crystallization of the magnetic calcium-iron layered double metal hydroxides and solidification of dissolved phosphorus are completed, and at the same time, decarbonated biogas is introduced from the bottom of the aging pool (when decarbonated biogas is insufficient, purified biogas is used for gas distribution), ammonia in the alkaline biogas is blown off, hydrogen sulfide in the decarbonated biogas is absorbed, and the biogas is blown off. The removed ammonia and ammonia produced in the nucleation pool are absorbed by the ammonia absorption tower to obtain recovered ammonia and purified biogas; the alkaline biogas slurry containing magnetic calcium iron layered double hydroxides is pumped from the aging tank into the magnetic sedimentation tank, and the magnetic calcium iron layered double hydroxides are rapidly precipitated under the action of the external magnetic field at the bottom of the tank, and then separated from the solid and liquid to obtain a solid magnetic calcium iron layered double hydroxide nanocomposite material; the upper alkaline clear liquid flows from the magnetic sedimentation tank into the alkaline water tank for storage; the alkaline clear liquid from the alkaline water tank is sprayed into the upper part of the decarbonization tower, and at the same time, the original biogas is introduced into the lower end of the decarbonization tower, and the carbon dioxide in the original biogas is absorbed by the alkaline biogas to generate solid calcium carbonate, and the pH value of the biogas slurry is reduced; the nearly neutral biogas slurry containing calcium carbonate is pumped into the sedimentation tank for calcium carbonate precipitation, and the bottom precipitate is separated from the solid and liquid to obtain solid calcium carbonate. This method can not only remove COD, ammonia nitrogen, total phosphorus in the biogas, as well as carbon dioxide and hydrogen sulfide in the biogas, but also produce high value-added products such as magnetic calcium-iron layered double hydroxide nanocomposites, calcium carbonate, ammonia fertilizer, etc., to achieve the effect of deep treatment of biogas, purification of biogas, and no sludge production.

[0025] To achieve the above purpose, Figure 1 As shown, the technical solutions adopted are as follows: A biogas purification method for biogas slurry deep treatment, the method comprising the following steps: a. The biogas slurry in the biogas slurry pool is pumped into the mixing tank, magnetic ferroferric oxide nanoparticles are added thereto, and the ferrous salt solution is pumped into the mixing tank from the dissolving tank 1, and the mixture is stirred quickly to evenly disperse the ferroferric oxide nanoparticles and mix the ferrous salt.

[0026] b. The biogas slurry flows from the mixing tank into the oxidation reaction tank, and the oxidant is pumped into the second drug dissolving tank, and stirred rapidly to carry out advanced oxidation reaction.

[0027] c. The sludge in which pollutants (organic pollutants, nitrogen-containing pollutants, and organic phosphorus) are oxidized and degraded flows from the oxidation reaction tank into the covered nucleation tank. Alkaline calcium reagent is pumped into the three-stage dissolution tank and stirred rapidly to carry out the nucleation reaction of magnetic calcium-iron layered double hydroxide.

[0028] d. Then it flows into the covered aging tank, and the decarbonized biogas from the decarbonization tower is introduced from the bottom of the tank to blow off the ammonia in the biogas. The sulfur in the biogas is absorbed, and the crystallization reaction of magnetic calcium-iron layered double metal hydroxide is carried out to solidify the inorganic phosphorus, iron and calcium in the biogas.

[0029] e. The decarbonized, desulfurized and ammonia-containing biogas enters the ammonia absorption tower from the aging tank, while the ammonia produced in the nucleation tank enters the ammonia absorption tower, and the acid liquid from the acid storage tank is sprayed into the tower from the top for ammonia absorption. The decarbonized, desulfurized and deammonified purified biogas enters the purified biogas storage tank. The liquid that absorbs ammonia in the ammonia absorption tower contains ammonium salts, which can be further processed into fertilizers.

[0030] f. The biogas slurry containing magnetic calcium iron layered double metal hydroxide is pumped from the aging tank into the magnetic sedimentation tank for precipitation of magnetic calcium iron layered double metal hydroxide. The bottom sediment enters the solid-liquid separator to separate the solid magnetic calcium iron layered double metal hydroxide. The calcium-containing alkaline biogas slurry at the top flows into the covered alkaline water tank for storage.

[0031] g. The original biogas in the original biogas storage tank is introduced from the bottom of the decarbonization tower, and the calcium-containing alkaline biogas liquid in the alkaline water pool is sprayed from the top of the decarbonization tower to absorb carbon dioxide and solidify the calcium in the liquid. The decarbonized biogas is introduced into the aging tank.

[0032] h. The purified biogas slurry containing calcium carbonate is pumped from the bottom of the decarbonization tower into the sedimentation tank. The bottom sediment enters the solid-liquid separator 2 to separate the solid calcium carbonate, and the biogas slurry with organic pollutants, nitrogen and phosphorus removed is in the upper part of the sedimentation tank, and the upper clear liquid is discharged / recycled.

[0033] The ferrous salt in step a is a soluble ferrous salt, such as ferrous chloride, ferrous nitrate, ferrous sulfate, etc. The soluble ferrous salt is first prepared into a concentrated solution in a dissolving tank 3, and then pumped into a mixing tank 2, and the concentration in the mixing tank 2 is ≥30mmol / L; the amount of ferrosoferric oxide nanoparticles added to the mixing tank 2 is 0.5-5 g / L; The mixing tank is provided with a stirring device, and the time for rapidly stirring and dispersing the nano-ferroferric oxide and mixing the ferrous salt is 2 to 10 minutes.

[0034] The reaction mechanism of producing magnetic calcium iron layered double hydroxide by using ferroferric oxide nanoparticles and alkaline calcium reagent is as follows: First, the divalent iron catalyzes the oxidant to undergo an advanced oxidation reaction to generate trivalent iron ions, and then an alkaline calcium reagent is added to provide sufficient divalent calcium ions and hydroxide (alkaline environment). Since the added magnetic nano-ferroferric oxide has an electronegative surface and a large specific surface area, it will react with trivalent iron, divalent calcium, and hydroxide ions on its surface through electrostatic adsorption and precipitation to generate a magnetic calcium-iron layered double metal hydroxide composite solid. At the same time, the anions in the biogas slurry (such as carbonate and phosphate) enter the interlayer of the calcium-iron layered double metal hydroxide through intercalation, thereby achieving the effect of removing phosphorus, iron, and calcium in the biogas slurry.

[0035] In step b, the oxidant is hydrogen peroxide, hypochlorite, persulfate, or peracetate, and the oxidant needs to be pre-prepared into a concentrated solution in the second drug dissolving tank; a stirring device is installed in the oxidation reaction tank; and the time for the advanced oxidation reaction is 10 to 30 minutes.

[0036] The alkaline calcium in step c is calcium oxide or calcium hydroxide, and the alkaline calcium needs to be pre-prepared into a slurry in the drug dissolving tank three; the molar ratio of the amount of alkaline calcium added in the nucleation tank to the amount of ferrous salt added in the mixing tank in step a is 2-4; the pH of the nucleation tank is maintained at 10-13; and the nucleation reaction time of the magnetic calcium iron layered double hydroxide is 5-20 min.

[0037] The nucleation pool is a covered closed pool, the top of the pool has an opening connected to the ammonia absorption tower through an alkali-resistant pipe, and the inner wall of the pool needs to be made of alkali-resistant material.

[0038] In the step d, the biogas from the nucleation tank flows into the aging tank from the upper end, and the hydraulic retention time is 40 to 100 minutes; the decarbonized biogas is introduced from the bottom of the aging tank through multiple evenly distributed porous tubes, and the gas-liquid volume ratio is 200 to 400:1, which can play a role of uniform and slow stirring, which is conducive to the rapid crystallization of magnetic calcium iron layered double metal hydroxides.

[0039] The aging tank is a covered closed tank, the top of the tank has an opening for a pipe connected to an ammonia absorption tower, and the inner wall of the tank needs to be made of alkali-resistant material.

[0040] In the step e, ammonia gas from the nucleation tank and the aging tank is introduced into the bottom of the ammonia absorption tower.

[0041] In the step f, a magnetic field is applied to the bottom of the magnetic sedimentation tank to quickly precipitate magnetic calcium iron layered double metal hydroxide solids; the hydraulic retention time of the biogas slurry in the magnetic sedimentation tank is 10 to 30 minutes; the inner wall of the magnetic sedimentation tank needs to be made of alkali-resistant materials; the inner wall of the alkaline water pool needs to be made of alkali-resistant materials, and the pool is covered and sealed to prevent absorption of carbon dioxide in the air.

[0042] In step g, the original biogas is introduced from the bottom of the decarbonization tower through multiple evenly distributed microporous tubes; the empty tower residence time of the original biogas is 0.5-2 min; and the pH value of the solution in the decarbonization tower is maintained at 7-9.

[0043] The amount of raw biogas introduced is adjusted according to the pH value of the liquid in the decarbonization tower, and the amount of introduction is controlled by a gas flow meter.

[0044] The biogas after decarbonation is discharged from the top of the decarbonization tower and enters the aging tank through the gas pipeline.

[0045] When the decarbonized biogas is insufficient, the decarbonized biogas is distributed from the purified biogas storage cabinet through gas flow meter 2, and the purified biogas pipeline distributed from the purified biogas storage cabinet is connected to the decarbonized biogas transportation pipeline, and a check valve is installed on the pipeline between the connection and the top of the decarbonization tower to prevent the distributed purified biogas from entering the decarbonization tower when the amount is large.

[0046] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0047] Example 1 A biogas purification method for biogas slurry deep treatment comprises the following steps: a. The biogas slurry in the biogas slurry tank 1 is pumped into the mixing tank 2, and magnetic ferroferric oxide nanoparticles are added thereto, and the ferrous salt solution is pumped into the mixing tank 2 from the drug dissolving tank 3, and the mixture is stirred rapidly to evenly disperse the ferroferric oxide nanoparticles and mix the ferrous salt.

[0048] b. The biogas slurry flows from the mixing tank 2 into the oxidation reaction tank 4, and the oxidant is pumped into the dissolving tank 5, and stirred rapidly to carry out an advanced oxidation reaction.

[0049] c. The biogas slurry in which pollutants are oxidized and degraded flows from the oxidation reaction tank 4 into the nucleation tank 6, and an alkaline calcium reagent is pumped into the solution tank 3 7, and stirred rapidly to carry out a nucleation reaction of the magnetic calcium iron layered double hydroxide.

[0050] d. Then it flows into the aging tank 8, and the decarbonized biogas from the decarbonization tower 12 is introduced from the bottom of the tank to blow off the ammonia in the biogas. The sulfur in the biogas is absorbed to obtain decarbonized, desulfurized, and ammonia-containing biogas, and the crystallization reaction of magnetic calcium-iron layered double metal hydroxide is carried out to solidify the inorganic phosphorus, iron and calcium in the biogas.

[0051] e. The decarbonized, desulfurized and ammonia-containing biogas enters the ammonia absorption tower 16 from the aging tank 8, and the ammonia generated by the nucleation tank 6 enters the ammonia absorption tower 16. The acid liquid from the acid storage tank 17 is sprayed from the top of the tower to absorb ammonia, thereby obtaining decarbonized, desulfurized and deammoniated purified biogas. The decarbonized, desulfurized and deammoniated purified biogas enters the purified biogas storage tank 18. The liquid that absorbs ammonia in the ammonia absorption tower 16 contains ammonium salts, which can be further processed into fertilizers.

[0052] f. The biogas slurry containing magnetic calcium-iron layered double metal hydroxide after the crystallization reaction is pumped from the aging tank 8 into the magnetic sedimentation tank 9 for precipitation of the magnetic calcium-iron layered double metal hydroxide, and the bottom precipitate enters a solid-liquid separator 10 to separate the solid magnetic calcium-iron layered double metal hydroxide, and the upper calcium-containing alkaline biogas slurry flows into the alkaline water tank 11 for storage.

[0053] g. The original biogas in the original biogas storage tank 15 is introduced from the bottom of the decarbonization tower 12, and the calcium-containing alkaline biogas slurry in the alkaline water pool 11 is sprayed from the top of the decarbonization tower 12 to absorb carbon dioxide and solidify the calcium in the liquid to obtain purified biogas containing calcium carbonate, and the decarbonized biogas is introduced into the aging tank 8.

[0054] h. The purified biogas slurry containing calcium carbonate is pumped from the bottom of the decarbonization tower 12 into the sedimentation tank 13. The bottom sediment enters the solid-liquid separator 14 to separate the solid calcium carbonate, and the biogas slurry with organic pollutants, nitrogen and phosphorus removed is in the upper part of the sedimentation tank 13, and the upper clear liquid is discharged / recycled.

[0055] The ferrous salt in step a is ferrous sulfate, and the concentration in the drug dissolving tank 3 is 8wt%, and then it is added to the mixing tank 2 using a drug adding pump, and the concentration in the mixing tank 2 is 80 mmol / L; the magnetic ferroferric oxide nanoparticles are directly added to the mixing tank 2, and the addition amount is 2 g / L. The stirring device in the mixing tank 2 stirs quickly to disperse the magnetic ferroferric oxide nanoparticles and mix the ferrous salt solution for 5 minutes, that is, the hydraulic retention time of the biogas slurry in the tank is 5 minutes.

[0056] In step b, the biogas slurry in the mixing tank 2 flows into the oxidation reaction tank 4 through the inter-tank channel. The oxidant is 30% hydrogen peroxide, which is pre-prepared into an 8 wt% solution in the dissolving tank 2 5. The prepared solution is added to the oxidation reaction tank 4 through a dosing pump, and stirred rapidly to perform an advanced oxidation reaction for 15 minutes, that is, the hydraulic retention time of the biogas slurry in the tank is 15 minutes.

[0057] In the step c, the biogas slurry in the oxidation reaction tank 4 flows into the nucleation tank 6 through the inter-tank channels. The alkaline calcium is calcium hydroxide, which is pre-prepared into a slurry with a concentration of 3 wt% in the dissolving tank 3 7. The amount of calcium hydroxide added to the nucleation tank 6 is 160 mmol / L, and the molar ratio of the amount of ferrous salt added to the mixing tank in step a is 2:1; at this time, the pH of the nucleation tank 6 is about 12.7. Rapid stirring in the tank allows the magnetic calcium-iron layered double metal hydroxide to rapidly nucleate for 20 minutes, that is, the hydraulic retention time of the biogas slurry in the tank is 20 minutes.

[0058] In the step d, the biogas from the nucleation pool 6 flows into the aging pool 8 from the upper end through the inter-pool channel. The hydraulic retention time of the biogas in the aging pool 8 is 60 min. The decarbonized biogas pipeline is connected to the purified biogas pipeline, and a check valve 21 is installed on the gas pipeline between the connection and the decarbonization tower 12 to prevent the purified biogas from entering the decarbonization tower 12 when the amount of distributed purified biogas is large. The decarbonized biogas and the purified biogas are introduced from the bottom end of the aging pool 8 through multiple evenly distributed porous tubes, with a gas-liquid volume ratio of 200:1.

[0059] The bottoms of the nucleation pool 6 and the aging pool 8 are connected to an ammonia delivery pipeline and lead to the bottom of the ammonia absorption tower 16 .

[0060] In step f, a hole is opened at the bottom of the aging tank 8, and a pump pumps out the alkaline biogas slurry containing solid magnetic calcium iron layered double metal hydroxide to the magnetic sedimentation tank 9 through the hole. A magnetic field is applied to the bottom of the magnetic sedimentation tank 9, and the precipitation time of the magnetic calcium iron layered double metal hydroxide is 30 minutes. The clear liquid at the top of the magnetic sedimentation tank 9 flows into the alkaline water tank 11 through the inter-tank channel.

[0061] In step g, the raw biogas is introduced from the bottom of the decarbonization tower 12 through multiple evenly distributed microporous tubes; the empty tower residence time of the raw biogas is 1.5 min; the pH of the solution in the decarbonization tower 12 is maintained at 7.5. The amount of raw biogas introduced is adjusted according to the pH of the liquid in the decarbonization tower, and the amount of introduction is controlled by a gas flow meter 19.

[0062] The biogas after decarbonation is discharged from the top of the decarbonization tower and enters the aging tank 8 through a gas pipeline equipped with a check valve 21.

[0063] When the decarbonized biogas is insufficient, the decarbonized biogas is distributed from the purified biogas storage cabinet through gas flow meter 2.

[0064] Example 2 A biogas purification method for biogas slurry deep treatment comprises the following steps: a. The biogas slurry in the biogas slurry tank 1 is pumped into the mixing tank 2, and magnetic ferroferric oxide nanoparticles are added thereto, and the ferrous salt solution is pumped into the mixing tank 2 from the drug dissolving tank 3, and the mixture is stirred rapidly to evenly disperse the ferroferric oxide nanoparticles and mix the ferrous salt.

[0065] b. The biogas slurry flows from the mixing tank 2 into the oxidation reaction tank 4, and the oxidant is pumped into the dissolving tank 5, and stirred rapidly to carry out an advanced oxidation reaction.

[0066] c. The biogas slurry in which pollutants are oxidized and degraded flows from the oxidation reaction tank 4 into the nucleation tank 6, and an alkaline calcium reagent is pumped into the solution tank 3 7, and stirred rapidly to carry out a nucleation reaction of the magnetic calcium iron layered double hydroxide.

[0067] d. Then it flows into the aging tank 8, and the decarbonized biogas from the decarbonization tower 12 is introduced from the bottom of the tank to blow off the ammonia in the biogas. The sulfur in the biogas is absorbed to obtain decarbonized, desulfurized, and ammonia-containing biogas, and a crystallization reaction of magnetic calcium-iron layered double metal hydroxide is carried out to solidify the inorganic phosphorus, iron, and calcium in the biogas.

[0068] e. The decarbonized, desulfurized and ammonia-containing biogas enters the ammonia absorption tower 16 from the aging tank 8, and the ammonia generated by the nucleation tank 6 enters the ammonia absorption tower 16. The acid liquid from the acid storage tank 17 is sprayed from the top of the tower to absorb ammonia, thereby obtaining decarbonized, desulfurized and deammoniated purified biogas. The decarbonized, desulfurized and deammoniated purified biogas enters the purified biogas storage tank 18. The liquid that absorbs ammonia in the ammonia absorption tower 16 contains ammonium salts, which can be further processed into fertilizers.

[0069] f. The biogas slurry containing magnetic calcium-iron layered double metal hydroxide after the crystallization reaction is pumped from the aging tank 8 into the magnetic sedimentation tank 9 for precipitation of the magnetic calcium-iron layered double metal hydroxide, and the bottom precipitate enters a solid-liquid separator 10 to separate the solid magnetic calcium-iron layered double metal hydroxide, and the upper calcium-containing alkaline biogas slurry flows into the alkaline water tank 11 for storage.

[0070] g. The original biogas in the original biogas storage tank 15 is introduced from the bottom of the decarbonization tower 12, and the calcium-containing alkaline biogas slurry in the alkaline water pool 11 is sprayed from the top of the decarbonization tower 12 to absorb carbon dioxide and solidify the calcium in the liquid to obtain purified biogas containing calcium carbonate, and the decarbonized biogas is introduced into the aging tank 8.

[0071] h. The purified biogas slurry containing calcium carbonate is pumped from the bottom of the decarbonization tower 12 into the sedimentation tank 13. The bottom sediment enters the solid-liquid separator 14 to separate the solid calcium carbonate, and the biogas slurry with organic pollutants, nitrogen and phosphorus removed is in the upper part of the sedimentation tank 13, and the upper clear liquid is discharged / recycled.

[0072] The ferrous salt in step a is ferrous chloride, and the concentration in the dissolving tank 3 is 8wt%, and then it is added to the mixing tank 2 using a dosing pump, and the concentration in the mixing tank 2 is 30 mmol / L; the magnetic ferroferric oxide nanoparticles are directly added to the mixing tank 2, and the addition amount is 0.5g / L. The stirring device in the mixing tank 2 stirs quickly to disperse the magnetic ferroferric oxide nanoparticles and mix the ferrous salt solution, and the time is 2 minutes, that is, the hydraulic retention time of the biogas slurry in the tank is 2 minutes.

[0073] In step b, the biogas slurry in the mixing tank 2 flows into the oxidation reaction tank 4 through the inter-tank channel. The oxidant is hypochlorite, which is pre-prepared into an 8 wt% solution in the dissolving tank 2 5. The prepared solution is added to the oxidation reaction tank 4 through a dosing pump, and stirred rapidly to perform an advanced oxidation reaction for 10 minutes, that is, the hydraulic retention time of the biogas slurry in the tank is 10 minutes.

[0074] In the step c, the biogas slurry in the oxidation reaction tank 4 flows into the nucleation tank 6 through the inter-tank pores. The alkaline calcium is calcium oxide, which is pre-prepared into a slurry with a concentration of 3 wt% in the dissolving tank 3 7. The amount of calcium oxide added to the nucleation tank 6 is 120 mmol / L, and the molar ratio of the amount of ferrous salt added to the mixing tank in step a is 4:1; at this time, the pH of the nucleation tank 6 is about 10. Rapid stirring in the tank allows the magnetic calcium iron layered double metal hydroxide to rapidly nucleate for 5 minutes, that is, the hydraulic retention time of the biogas slurry in the tank is 5 minutes.

[0075] In the step d, the biogas from the nucleation pool 6 flows into the aging pool 8 from the upper end through the inter-pool channel. The hydraulic retention time of the biogas in the aging pool 8 is 40 min. The decarbonized biogas pipeline is connected to the purified biogas pipeline, and a check valve 21 is installed on the gas pipeline between the connection and the decarbonization tower 12 to prevent the purified biogas from entering the decarbonization tower 12 when the amount of distributed purified biogas is large. The decarbonized biogas and the purified biogas are introduced from the bottom end of the aging pool 8 through multiple evenly distributed porous tubes, with a gas-liquid volume ratio of 300:1.

[0076] The bottoms of the nucleation pool 6 and the aging pool 8 are connected to an ammonia delivery pipeline and lead to the bottom of the ammonia absorption tower 16 .

[0077] In step f, a hole is opened at the bottom of the aging tank 8, and a pump pumps out the alkaline biogas slurry containing solid magnetic calcium iron layered double metal hydroxide to the magnetic sedimentation tank 9 through the hole. A magnetic field is applied to the bottom of the magnetic sedimentation tank 9, and the precipitation time of the magnetic calcium iron layered double metal hydroxide is 10 minutes. The clear liquid at the top of the magnetic sedimentation tank 9 flows into the alkaline water tank 11 through the inter-tank channel.

[0078] In step g, the raw biogas is introduced from the bottom of the decarbonization tower 12 through multiple evenly distributed microporous tubes; the empty tower residence time of the raw biogas is 0.5 min; the pH of the solution in the decarbonization tower 12 is maintained at 7. The amount of raw biogas introduced is adjusted according to the pH of the liquid in the decarbonization tower, and the amount of introduction is controlled by a gas flow meter 19.

[0079] The biogas after decarbonation is discharged from the top of the decarbonization tower and enters the aging tank 8 through a gas pipeline equipped with a check valve 21.

[0080] When the decarbonized biogas is insufficient, the decarbonized biogas is distributed from the purified biogas storage cabinet through gas flow meter 2.

[0081] Example 3 A biogas purification method for biogas slurry deep treatment comprises the following steps: a. The biogas slurry in the biogas slurry tank 1 is pumped into the mixing tank 2, and magnetic ferroferric oxide nanoparticles are added thereto, and the ferrous salt solution is pumped into the mixing tank 2 from the drug dissolving tank 3, and the mixture is stirred rapidly to evenly disperse the ferroferric oxide nanoparticles and mix the ferrous salt.

[0082] b. The biogas slurry flows from the mixing tank 2 into the oxidation reaction tank 4, and the oxidant is pumped into the dissolving tank 5, and stirred rapidly to carry out an advanced oxidation reaction.

[0083] c. The biogas slurry in which pollutants are oxidized and degraded flows from the oxidation reaction tank 4 into the nucleation tank 6, and an alkaline calcium reagent is pumped into the solution tank 3 7, and stirred rapidly to carry out a nucleation reaction of the magnetic calcium iron layered double hydroxide.

[0084] d. Then it flows into the aging tank 8, and the decarbonized biogas from the decarbonization tower 12 is introduced from the bottom of the tank to blow off the ammonia in the biogas. The sulfur in the biogas is absorbed to obtain decarbonized, desulfurized, and ammonia-containing biogas, and a crystallization reaction of magnetic calcium iron layered double metal hydroxide is carried out to solidify the inorganic phosphorus in the biogas.

[0085] e. The decarbonized, desulfurized and ammonia-containing biogas enters the ammonia absorption tower 16 from the aging tank 8, and the ammonia generated by the nucleation tank 6 enters the ammonia absorption tower 16. The acid liquid from the acid storage tank 17 is sprayed from the top of the tower to absorb ammonia, thereby obtaining decarbonized, desulfurized and deammoniated purified biogas. The decarbonized, desulfurized and deammoniated purified biogas enters the purified biogas storage tank 18. The liquid that absorbs ammonia in the ammonia absorption tower 16 contains ammonium salts, which can be further processed into fertilizers.

[0086] f. The biogas slurry containing magnetic calcium-iron layered double metal hydroxide after the crystallization reaction is pumped from the aging tank 8 into the magnetic sedimentation tank 9 for precipitation of the magnetic calcium-iron layered double metal hydroxide, and the bottom precipitate enters a solid-liquid separator 10 to separate the solid magnetic calcium-iron layered double metal hydroxide, and the upper calcium-containing alkaline biogas slurry flows into the alkaline water tank 11 for storage.

[0087] g. The original biogas in the original biogas storage tank 15 is introduced from the bottom of the decarbonization tower 12, and the calcium-containing alkaline biogas slurry in the alkaline water pool 11 is sprayed from the top of the decarbonization tower 12 to absorb carbon dioxide and solidify the calcium in the liquid to obtain purified biogas containing calcium carbonate, and the decarbonized biogas is introduced into the aging tank 8.

[0088] h. The purified biogas slurry containing calcium carbonate is pumped from the bottom of the decarbonization tower 12 into the sedimentation tank 13. The bottom sediment enters the solid-liquid separator 14 to separate the solid calcium carbonate, and the biogas slurry with organic pollutants, nitrogen and phosphorus removed is in the upper part of the sedimentation tank 13, and the upper clear liquid is discharged / recycled.

[0089] The ferrous salt in step a is ferrous nitrate, and the concentration in the drug dissolving tank 3 is 8 wt%, and then added to the mixing tank 2 using a drug adding pump, and the concentration in the mixing tank 2 is 60 mmol / L; the magnetic ferroferric oxide nanoparticles are directly added to the mixing tank 2, and the addition amount is 3 g / L. The stirring device in the mixing tank 2 stirs quickly to disperse the magnetic ferroferric oxide nanoparticles and mix the ferrous salt solution for 6 minutes, that is, the hydraulic retention time of the biogas slurry in the tank is 6 minutes.

[0090] In step b, the biogas slurry in the mixing tank 2 flows into the oxidation reaction tank 4 through the inter-tank channels. The oxidant is persulfate, which is pre-prepared into an 8 wt% solution in the dissolving tank 2 5. The prepared solution is added to the oxidation reaction tank 4 through a dosing pump, and stirred rapidly to perform an advanced oxidation reaction for 20 minutes, that is, the hydraulic retention time of the biogas slurry in the tank is 20 minutes.

[0091] In the step c, the biogas slurry in the oxidation reaction tank 4 flows into the nucleation tank 6 through the inter-tank channels. The alkaline calcium is calcium oxide, which is pre-prepared into a slurry with a concentration of 3 wt% in the dissolving tank 3 7. The amount of calcium oxide added to the nucleation tank 6 is 180 mmol / L, and the molar ratio of the amount of ferrous salt added to the mixing tank in step a is 3:1; at this time, the pH of the nucleation tank 6 is about 11.5. Rapid stirring in the tank allows the magnetic calcium iron layered double metal hydroxide to rapidly nucleate for 15 minutes, that is, the hydraulic retention time of the biogas slurry in the tank is 15 minutes.

[0092] In the step d, the biogas from the nucleation pool 6 flows into the aging pool 8 from the upper end through the inter-pool channel. The hydraulic retention time of the biogas in the aging pool 8 is 80 min. The decarbonized biogas pipeline is connected to the purified biogas pipeline, and a check valve 21 is installed on the gas pipeline between the connection and the decarbonization tower 12 to prevent the purified biogas from entering the decarbonization tower 12 when the amount of distributed purified biogas is large. The decarbonized biogas and the purified biogas are introduced from the bottom end of the aging pool 8 through multiple evenly distributed porous tubes, with a gas-liquid volume ratio of 200:1.

[0093] The bottoms of the nucleation pool 6 and the aging pool 8 are connected to an ammonia delivery pipeline and lead to the bottom of the ammonia absorption tower 16 .

[0094] In step f, a hole is opened at the bottom of the aging tank 8, and a pump pumps out the alkaline biogas slurry containing solid magnetic calcium iron layered double metal hydroxide to the magnetic sedimentation tank 9 through the hole. A magnetic field is applied to the bottom of the magnetic sedimentation tank 9, and the precipitation time of the magnetic calcium iron layered double metal hydroxide is 20 minutes. The clear liquid at the top of the magnetic sedimentation tank 9 flows into the alkaline water tank 11 through the inter-tank channel.

[0095] In step g, the raw biogas is introduced from the bottom of the decarbonization tower 12 through multiple evenly distributed microporous tubes; the empty tower residence time of the raw biogas is 1 min; the pH of the solution in the decarbonization tower 12 is maintained at 7. The amount of raw biogas introduced is adjusted according to the pH of the liquid in the decarbonization tower, and the amount of introduction is controlled by a gas flow meter 19.

[0096] The biogas after decarbonation is discharged from the top of the decarbonization tower and enters the aging tank 8 through a gas pipeline equipped with a check valve 21.

[0097] When the decarbonized biogas is insufficient, the decarbonized biogas is distributed from the purified biogas storage cabinet through gas flow meter 2.

[0098] Example 4 A biogas purification method for biogas slurry deep treatment comprises the following steps: a. The biogas slurry in the biogas slurry tank 1 is pumped into the mixing tank 2, and magnetic ferroferric oxide nanoparticles are added thereto, and the ferrous salt solution is pumped into the mixing tank 2 from the drug dissolving tank 3, and the mixture is stirred rapidly to evenly disperse the ferroferric oxide nanoparticles and mix the ferrous salt.

[0099] b. The biogas slurry flows from the mixing tank 2 into the oxidation reaction tank 4, and the oxidant is pumped into the dissolving tank 5, and stirred rapidly to carry out an advanced oxidation reaction.

[0100] c. The biogas slurry in which pollutants are oxidized and degraded flows from the oxidation reaction tank 4 into the nucleation tank 6, and an alkaline calcium reagent is pumped into the solution tank 3 7, and stirred rapidly to carry out a nucleation reaction of the magnetic calcium iron layered double hydroxide.

[0101] d. Then it flows into the aging tank 8, and the decarbonized biogas from the decarbonization tower 12 is introduced from the bottom of the tank to blow off the ammonia in the biogas. The sulfur in the biogas is absorbed to obtain decarbonized, desulfurized, and ammonia-containing biogas, and a crystallization reaction of magnetic calcium-iron layered double metal hydroxide is carried out to solidify the inorganic phosphorus, iron, and calcium in the biogas.

[0102] e. The decarbonized, desulfurized and ammonia-containing biogas enters the ammonia absorption tower 16 from the aging tank 8, and the ammonia generated by the nucleation tank 6 enters the ammonia absorption tower 16. The acid liquid from the acid storage tank 17 is sprayed from the top of the tower to absorb ammonia, thereby obtaining decarbonized, desulfurized and deammoniated purified biogas. The decarbonized, desulfurized and deammoniated purified biogas enters the purified biogas storage tank 18. The liquid that absorbs ammonia in the ammonia absorption tower 16 contains ammonium salts, which can be further processed into fertilizers.

[0103] f. The biogas slurry containing magnetic calcium-iron layered double metal hydroxide after the crystallization reaction is pumped from the aging tank 8 into the magnetic sedimentation tank 9 for precipitation of the magnetic calcium-iron layered double metal hydroxide, and the bottom precipitate enters a solid-liquid separator 10 to separate the solid magnetic calcium-iron layered double metal hydroxide, and the upper calcium-containing alkaline biogas slurry flows into the alkaline water tank 11 for storage.

[0104] g. The original biogas in the original biogas storage tank 15 is introduced from the bottom of the decarbonization tower 12, and the calcium-containing alkaline biogas slurry in the alkaline water pool 11 is sprayed from the top of the decarbonization tower 12 to absorb carbon dioxide and solidify the calcium in the liquid to obtain purified biogas containing calcium carbonate, and the decarbonized biogas is introduced into the aging tank 8.

[0105] h. The purified biogas slurry containing calcium carbonate is pumped from the bottom of the decarbonization tower 12 into the sedimentation tank 13. The bottom sediment enters the solid-liquid separator 14 to separate the solid calcium carbonate, and the biogas slurry with organic pollutants, nitrogen and phosphorus removed is in the upper part of the sedimentation tank 13, and the upper clear liquid is discharged / recycled.

[0106] The ferrous salt in step a is ferrous nitrate, and the concentration in the drug dissolving tank 3 is 8wt%, and then added to the mixing tank 2 using a drug adding pump, and the concentration in the mixing tank 2 is 80 mmol / L; the magnetic ferroferric oxide nanoparticles are directly added to the mixing tank 2, and the addition amount is 5 g / L. The stirring device in the mixing tank 2 stirs rapidly to disperse the magnetic ferroferric oxide nanoparticles and mix the ferrous salt solution, and the time is 10 minutes, that is, the hydraulic retention time of the biogas slurry in the tank is 10 minutes.

[0107] In step b, the biogas slurry in the mixing tank 2 flows into the oxidation reaction tank 4 through the inter-tank channels. The oxidant is peracetate, which is pre-prepared into an 8 wt% solution in the dissolving tank 2 5. The prepared solution is added to the oxidation reaction tank 4 through a dosing pump, and stirred rapidly to perform an advanced oxidation reaction for 30 minutes, that is, the hydraulic retention time of the biogas slurry in the tank is 30 minutes.

[0108] In the step c, the biogas slurry in the oxidation reaction tank 4 flows into the nucleation tank 6 through the inter-tank pores. The alkaline calcium is calcium hydroxide, which is pre-prepared into a slurry with a concentration of 3 wt% in the dissolving tank 3 7. The amount of calcium hydroxide added to the nucleation tank 6 is 160 mmol / L, and the molar ratio of the amount of ferrous salt added to the mixing tank in step a is 2:1; at this time, the pH of the nucleation tank 6 is about 13. Rapid stirring in the tank allows the magnetic calcium-iron layered double metal hydroxide to rapidly nucleate for 20 minutes, that is, the hydraulic retention time of the biogas slurry in the tank is 20 minutes.

[0109] In the step d, the biogas from the nucleation pool 6 flows into the upper end of the aging pool 8 through the inter-pool channel. The hydraulic retention time of the biogas in the aging pool 8 is 100 min. The decarbonized biogas pipeline is connected to the purified biogas pipeline, and a check valve 21 is installed in the gas pipeline between the connection and the decarbonization tower 12 to prevent the purified biogas from entering the decarbonization tower 12 when the amount of distributed purified biogas is large. The decarbonized biogas and the purified biogas are introduced from the bottom end of the aging pool 8 through multiple evenly distributed porous tubes, with a gas-liquid volume ratio of 400:1.

[0110] The bottoms of the nucleation pool 6 and the aging pool 8 are connected to an ammonia delivery pipeline and lead to the bottom of the ammonia absorption tower 16 .

[0111] In step f, a hole is opened at the bottom of the aging tank 8, and a pump pumps out the alkaline biogas slurry containing solid magnetic calcium iron layered double metal hydroxide to the magnetic sedimentation tank 9 through the hole. A magnetic field is applied to the bottom of the magnetic sedimentation tank 9, and the precipitation time of the magnetic calcium iron layered double metal hydroxide is 30 minutes. The clear liquid at the top of the magnetic sedimentation tank 9 flows into the alkaline water tank 11 through the inter-tank channel.

[0112] In step g, the raw biogas is introduced from the bottom of the decarbonization tower 12 through multiple evenly distributed microporous tubes; the empty tower residence time of the raw biogas is 2 min; the pH of the solution in the decarbonization tower 12 is maintained at 9. The amount of raw biogas introduced is adjusted according to the pH of the liquid in the decarbonization tower, and the amount of introduction is controlled by a gas flow meter 19.

[0113] The biogas after decarbonation is discharged from the top of the decarbonization tower and enters the aging tank 8 through a gas pipeline equipped with a check valve 21.

[0114] When the decarbonized biogas is insufficient, the decarbonized biogas is distributed from the purified biogas storage cabinet through the gas flow meter 2; It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0115] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0116] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any ordinary technician in the industry can smoothly implement the present invention as shown in the drawings and described above. However, any equivalent changes, modifications and evolutions made by technicians familiar with the profession without departing from the scope of the technical solution of the present invention using the technical content disclosed above are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. A method for deep treatment of biogas slurry combined with biogas purification, characterized in that: include: S1. Adding ferroferric oxide, ferrous salt solution and oxidant to biogas slurry to generate advanced oxidation reaction, thereby degrading pollutants in biogas slurry, then adding alkaline calcium reagent to perform nucleation reaction of magnetic calcium iron layered double metal hydroxide, then introducing decarbonized biogas to blow off ammonia in biogas slurry, and after sulfur in biogas is absorbed, obtaining decarbonized, desulfurized and ammonia-containing biogas, and performing crystallization reaction of magnetic calcium iron layered double metal hydroxide to solidify inorganic phosphorus, iron and calcium in biogas slurry; S2, mixing the decarbonized, desulfurized, ammonia-containing biogas with the ammonia generated by the nucleation reaction and then performing ammonia absorption treatment with an acid solution to obtain decarbonized, desulfurized, and deammonified purified biogas; S3, after the biogas slurry after the crystallization reaction is precipitated, the solid magnetic calcium iron layered double metal hydroxide is separated from the bottom precipitate, the upper calcium-containing alkaline biogas and the original biogas are subjected to carbon dioxide absorption to obtain decarbonized biogas, and the calcium in the calcium-containing alkaline biogas is solidified to obtain purified biogas containing calcium carbonate; S4. Separate the solid calcium carbonate from the bottom sediment in the purified biogas slurry containing calcium carbonate, and obtain the upper layer of biogas slurry with organic pollutants, nitrogen and phosphorus removed, which is discharged / recycled, thereby achieving deep treatment of biogas slurry combined with biogas purification.

2. The method for deep treatment of biogas slurry combined with biogas purification according to claim 1, characterized in that: The ferroferric oxide is a magnetic ferroferric oxide nanoparticle; the ferrous salt is one of ferrous chloride, ferrous nitrate and ferrous sulfate; the oxidant is one of hydrogen peroxide, hypochlorite, persulfate and peracetic acid; The molar concentration of the ferrous salt solution is greater than or equal to 30 mmol / L; the amount of ferroferric oxide added is 0.5-5 g / L; the alkaline calcium reagent is calcium oxide or calcium hydroxide; and the molar ratio of the alkaline calcium reagent to the ferrous salt is 2-4:

1.

3. The method for deep treatment of biogas slurry combined with biogas purification according to claim 1, characterized in that: The time of the advanced oxidation reaction is 10-30 min, the time of the nucleation reaction is 5-20 min, the pH of the nucleation reaction is 10-13, the time of the crystallization reaction is 40-100 min, the time of the biogas slurry precipitation after the crystallization reaction is 10-30 min, and the volume ratio of the decarbonized biogas to the biogas slurry is 200-400:

1.

4. A biogas slurry deep treatment combined with biogas purification system, based on the biogas slurry deep treatment combined with biogas purification method according to any one of claims 1 to 3, characterized in that: include: A biogas tank (1), a mixing tank (2), an oxidation reaction tank (4), a nucleation tank (6), an aging tank (8), a magnetic sedimentation tank (9), an alkaline water tank (11), a decarbonization tower (12), a sedimentation tank (13), a raw biogas storage tank (15), an ammonia absorption tower (16), an acid storage tank (17), and a purified biogas storage tank (18); The biogas slurry pool (1) is connected in sequence to a mixing pool (2), an oxidation reaction pool (4), a nucleation pool (6), an aging pool (8), a magnetic sedimentation pool (9), an alkaline water pool (11), a decarbonization tower (12) and a sedimentation pool (13); The bottom of the aging tank (8) is connected to the top of the decarbonization tower (12) through a pipeline; the top of the nucleation tank (6) and the aging tank (8) are connected to the bottom of the ammonia absorption tower (16); the acid storage tank (17) is connected to the ammonia absorption tower (16); The purified biogas storage tank (18) is connected to the ammonia absorption tower (16); the raw biogas storage tank (15) is connected to the bottom of the decarbonization tower (12); The mixing pool (2) is connected to the drug dissolving pool 1 (3) via a pipeline; the oxidation reaction pool (4) is connected to the drug dissolving pool 2 (5) via a pipeline; and the nucleation pool (6) is connected to the drug dissolving pool 3 (7) via a pipeline.

5. A biogas purification system for deep biogas treatment of biogas slurry according to claim 4, characterized in that: The nucleation pool (6) is a covered closed pool, a through hole is provided on the top of the nucleation pool (6), and the pool is connected to the ammonia absorption tower (16) through an alkali-resistant pipe, and the inner wall of the nucleation pool (6) is made of an alkali-resistant material; the aging pool (8) is a covered closed pool, a through hole is provided on the top of the aging pool (8), and the pool is connected to the ammonia absorption tower (16) through an alkali-resistant pipe, and the inner wall of the aging pool (8) is made of an alkali-resistant material; the alkaline water pool (11) is a covered closed pool, and the inner wall of the alkaline water pool (11) is made of an alkali-resistant material.

6. The biogas purification system for biogas slurry deep treatment according to claim 4, characterized in that: The top pipeline of the decarbonization tower (12) is connected to the decarbonization biogas pipeline of the aging tank (8) and the purified biogas pipeline of the purified biogas storage cabinet (18), and a check valve (21) is installed between the connection and the decarbonization tower (12); A gas flow meter 1 (19) is provided on the connecting pipeline between the raw biogas storage tank (15) and the decarbonization tower (12); A gas flow meter 2 (20) is provided on the connecting pipeline between the purified biogas storage cabinet (18) and the aging tank (8); The bottom of the magnetic sedimentation tank (9) is connected to a solid-liquid separator 1 (10); the bottom of the sedimentation tank (13) is connected to a solid-liquid separator 2 (14).

7. The biogas purification system for biogas slurry deep treatment according to claim 4, characterized in that: A magnetic field is arranged at the bottom of the magnetic sedimentation tank (9).

8. The biogas purification system for biogas slurry deep treatment according to claim 4, characterized in that: The decarbonized biogas and the purified biogas are introduced into the bottom of the aging tank (8), and the internal pipes for introducing the decarbonized biogas and the purified biogas into the bottom of the aging tank (8) are a plurality of evenly distributed porous pipes.

9. The biogas purification system for biogas slurry deep treatment according to claim 4, characterized in that: The raw biogas in the raw biogas storage tank (15) is introduced into the bottom of the decarbonization tower (12), and the internal pipeline for introducing the raw biogas into the bottom of the decarbonization tower (12) is a plurality of multi-microporous tubes; the empty tower residence time of the raw biogas in the decarbonization tower (12) is 0.5-2 min; and the pH value of the solution in the decarbonization tower (12) is maintained at 7-9.

10. The biogas purification system for biogas slurry deep treatment according to claim 4, characterized in that: When the decarbonized biogas in the decarbonization tower (12) is insufficient, the decarbonized biogas is distributed from the purified biogas storage tank (18) through the second gas flow meter (20).

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